Shown in FIG. 1 is a side view of a conventional underwing aircraft turbofan engine 10 surrounded by a number of annular members. Shown in FIG. 1 is a nacelle barrel 11, a fan cowl 12, a cascade-type thrust reverser 13, an aft engine cowl 14, and a primary exhaust nozzle cone 15. It frequently occurs that one or more of these annual members are formed of opposed semi-circular portions hinged to an upper strut or support pylon. During maintenance, the opposed halves are rotated outward to allow a mechanic access to the engine.
FIG. 2 illustrates cross-sectional portions of the aft cowl in FIG. 1. In this configuration, both the aft cowl and the thrust reverser are formed from opposed semi-circular halves, and are additionally connected so as to rotated in unison. During maintenance, each combination rotates about an axis referred to as its thrust reverser hinge line 16, 16' that is located generally above its respective aft cowl half. See FIG. 2.
The configuration of FIG. 2 includes one or more hoop-tie band assemblies 17, 17' contained within each aft cowl half for the purpose of providing a hoop load continuity to the aft cowl when closed. "Hoop load" refers to the load in a continuous object around a circular member or members, e.g., a hoop load would exist in the metal band surrounding the staves of a barrel. In the case of the aft engine cowl halves, the hoop-tie band assemblies include straps or bands 11, 11', a cross-tie link 13, and a number of latches 18, 18', 18". These components form a continuous load path around the aft cowl that is capable of reacting over pressurization of the necelle structure.
The kinematic arrangement required by the thrust reverser hinge line of this particular embodiment, requires the aft cowl hoop-tie bands to travel at a differential rate relative to that of the thrust reverser halves. In a closed position, current configurations requires latching of the hoop-tie band assemblies not only to their respective aft cowl half, but additionally latching of the aft cowl halves together. Still referring to FIG. 2, current cowl designs utilize three separate latches 18, 18', and 18" at each hoop-tie location. There are typically two hoop-tie locations per nacelle, requiring a total of six latches per engine. If any one of these latches is not completely unlatched during maintenance, subsequent opening of a thrust reverser half may cause damage to the hoop-tie assembly and/or the thrust reverser structure.
Thus, a need exists for an improved latch assembly for use in securely joining opposed arcuate members surrounding an aircraft engine, such as the hoop-tie assembly of a nacelle aft cowl. The ideal mechanism would reduce or eliminate the likelihood of damage to the aft cowls and/or thrust reverser structure should the operator attempt to open the thrust reverser without having the aft cowl latches fully opened. The ideal mechanism would further require fewer parts and less work to latch and unlatch. The present invention is directed to fulfilling this need.